microwave

1. 4 IEEE PHOTONICS SOCIETY NEWSLETTER April 2012
Research Highlights
A Tutorial on Microwave Photonics
Jianping Yao, Microwave Photonics Research Laboratory, School of Electrical
Engineering and Computer Science, University of Ottawa, Canada K1N 6N5
Abstract – The broad bandwidth and low loss offered by mod-
ern photonics have led to an ever-increasing interest in the
design and implementation of photonically assisted solutions
for the generation, processing, control and distribution of mi-
crowave signals, an area called microwave photonics. In this
article, a tutorial on microwave photonics is presented with an
emphasis on optical generation of microwave signals and all-
optical microwave signal processing.
Introduction
Microwave photonics is an area that studies the interaction
between microwave and optical waves for application such
as radar, communications, sensor networks, warfare systems
and instrumentation. In the past few years, there has been an
increasing effort in researching new microwave photonic so-
lutions for these applications [1]. In general, the microwave
photonics techniques cover the following topics: 1) photonic
generation of microwave signals, 2) photonic processing of
microwave signals, 3) photonic distribution of microwave
signals, and 4) photonic analog-to-digital conversion. In this
article, techniques developed in the last few years are reviewed
with an emphasis on the system architectures to implement
the functions for the photonic generation, and processing of
microwave signals.
Optical Generation
of Microwave Signals
A high frequency and frequency-tunable microwave signal can
be generated by beating two optical waves at a photodetector
(PD), as shown in Fig.1. Assume we have two optical waves
given by
cos( t( ) ,E t E )11 01 1+~ z= (1)
and
cos( t( ) ,E t E )22 02 2+~ z= (2)
where ,E01 E02 are the amplitude terms and 1z , 2z are the
phase terms of the two optical waves. The signal at the output
of the PD is given by
( ) | ( )| | ( ) ( )|I t R E t R E t E t2
1 2
2
= = + =
[( ) ( )]cosRP RP R P P t21 2 1 2 1 2 1 2~ ~ z z+ + - + - (3)
where R is the responsivity of the PD. Considering the limited band-
width of the PD, the current at the output of the PD is given by
[( ) ( )],cosI R P P t2RF 1 2 1 2 1 2~ ~ z z= - + - (4)
As can be seen from (4), a microwave signal with a frequen-
cy equal to the frequency difference between the two optical
waves is generated. This technique is capable of generating an
electrical signal with a frequency up to the THz band, limited
only by the bandwidth of the PD. However, by beating two
optical waves from two free-running LDs would lead to a mi-
crowave signal having high phase noise since the phase terms
of the two optical waves are not correlated, and the beating
process will transfer the phase noise of the two optical waves
to the generated microwave signal. Numerous techniques have
been proposed in the last few years to generate low-phase-noise
microwave signals with the two optical waves being locked
in phase. These techniques can be classified into three catego-
ries: 1) Optical injection locking, 2) Optical phase-lock loop
(OPLL), and 3) Microwave generation using external modula-
tion. In addition, a low-phase-noise microwave signal can also
be generated using an opto-electronic oscillator (OEO).
Optical Injection Locking
To generate a high-quality microwave signal via heterodyning,
the phase terms of the two optical waves used for heterodyning
must be highly correlated. A solution is to lock the phase terms
of two optical waves via optical injection locking [2] [3]. Fig.
2 shows a scheme to achieve optical injection locking, in which
a master laser diode (LD) is frequency-modulated by an micro-
wave at ,fm and the output from the master LD, consisting of an
optical carrier at ,0m two first-order sidebands and other high-
er-order sidebands, is injected into the slave LDs. The two slave
LDs have a free-running wavelengths close to the wavelengths
of two sideband, say -2nd and +2nd order sidebands, thus
the two slave LDs are injection locked, and the optical waves at
the outputs of the two slave LDs are phase correlated and the
beating of the two waves would generate a microwave signal
ω1
ω2
ω1–ω2
Optical
Coupler
RF Output
LD1
PD
LD2
Figure 1. Beating of two optical waves at a PD for the genera-
tion of a microwave signal.

2. April 2012 IEEE PHOTONICS SOCIETY NEWSLETTER 5
with its phase noise determined by the
reference RF source. Note that the sys-
tem can achieve frequency multiplying
operation. For the configuration shown
in Fig. 2, the generated frequency is four
times the frequency of the reference RF
source, a frequency quadrupling opera-
tion is thus achieved. Note also that the
microwave signal can generated remotely.
This is the key motivation of using such
a technique for the optical distribution of
microwave signals.
Optical Phase Lock Loop
Two free-running laser sources can also
be phase locked using a phase lock loop
[4]–[10]. Fig. 3 shows a scheme to achieve optical phase lock-
ing of two LDs. As can be seen two optical waves from two LDs
are applied to a PD. At the output of the PD, a beat note with
the frequency corresponding to the wavelength spacing is gen-
erated. The generated microwave signal is then sent to a phase
detector consisting of an electronic mixer and a low-pass filter.
The output voltage, which is proportional to the phase differ-
ence between the generated microwave signal and the reference
signal, is sent to one LD to control the injection current, and
thus its phase is accordingly changed, leading to the lock of the
phase terms of the two optical waves.
The locking range is determined by the linewidth of the
LDs and the loop length. To achieve affective phase lock-
ing, we need to use narrow linewidth LDs and also to make
the loop length shorter. Again, similar to the injection lock-
ing scheme, the optical signal can be distributed over opti-
cal fiber for remote distribution. Note that it is not necessary
that the frequency of the RF reference source is identical to
the frequency of the generated microwave signal. In fact, if
a harmonic generator is used, then a RF signal with differ-
ent orders of harmonics can be sent to the mixer, thus a rela-
tively low frequency RF reference signal can be used. For ex-
ample, to generate a 60 GHz microwave signal, one may use a
15-GHz reference source, and the fourth harmonic will be
mixed with the beat note to produce a voltage signal to control
the phase of one LD.
Microwave Generation Based
on External Modulation
Microwave signal generation can also be implemented
based on external modulation, by which the frequency of a
low-frequency microwave signal can be increased to a high
frequency through frequency multiplication [11][12].
Fig. 4(a) shows a scheme to achieve frequency doubling
using a Mach-Zehnder modulator (MZM). A RF signal is
applied to the MZM via the RF port. The MZM is biased
at the minimum transmission point (MITP) to suppress
the optical carrier. At the output of the MZM, only two
first-order sidebands are generated. By beating the first-
order sidebands at a PD, a frequency doubled microwave
signal is generated.
If the MZM is biased at the maximum transmission point
(MATP), at the output of the MZM, an optical signal with an
optical carrier and two second-order sidebands are generated.
By using a notch filter to remove the optical carrier, and then
beat the two sidebands at the PD, a frequency quadrupled mi-
crowave signal is generated.
To generate a microwave signal with a higher multiplica-
tion factor, a configuration that employs two cascaded MZMs
may be used. The multiplication factor can be as high as 12,
which enables the generation of a high frequency microwave
or terahertz signal using a low-frequency microwave source.
Different techniques have been proposed for the generation
λ0 λ0Slave LD1
PD
fm 4fm
4fmfm
Slave LD2
Optical Fiber
RF Master LD
Isolator
FM-modulated Master Laser
Slave Laser 2 Slave Laser 1
Figure 2. Optical injection locking of two slave LDs.
PD
RF
Mixer
Loop Control
Loop
Filter
Phase Detector
LD1
LD2 Remote Site Harmonic
Generator
fm
fm/N
Amplifier
Figure 3. Optical phase locking of two LDs using a phase lock loop. The mixer, the am-
plifier and the loop filter forms a phase detection module.

3. 6 IEEE PHOTONICS SOCIETY NEWSLETTER April 2012
of a frequency-quadrupled [13]–[15], sextupled [16]–[18],
octupled [19]–[22] and twelvetupled [23] microwave sig-
nal. All these approaches were implemented by biasing the
MZMs at the MATP or MITP in conjunction with the use
of an optical or microwave phase shifter and an optical filter.
For two cascaded MZMs, there are four possible bias combi-
nations: 1) MATP, MATP, 2) MITP, MITP, 3) MATP, MITP,
and 4) MITP, MATP, with each combination corresponding
to a specific multiplication factor under different operation
conditions. Fig. 5 shows a microwave generation system us-
ing two cascaded MZMs. A theoretical analysis leading to
the operating conditions to achieve frequency quadrupling,
sextupling, and octupling was developed and verified experi-
mentally [22].
Microwave Generation Based
on an Electro-Optic Oscillator
In addition to the beating of two optical
waves at a PD to generate a microwave
signal, a high spectral purity microwave
signal can also be generated using an
opto-electronic oscillator (OEO) [24].
Compared with the techniques using
injection locking, phase-lock loop or
external modulation, the use of an OEO
can generate a microwave signal with-
out the need for a reference microwave
source. Fig. 6 shows a typical OEO. If
the gain in the loop is greater than the
loss, the OEO will oscillate. The phase
noise performance is determined by the
Q factor of the OEO loop. To generate a microwave signal with
low phase noise, the loop length should be long, from a few
to tens of km. The use of a long loop length will, however,
cause the OEO to generate a large number of closely spaced
eigenmodes. To ensure a single-frequency oscillation, a high Q
microwave filter with an ultra-narrow bandwidth must be used
or high level of side modes will be generated. The use of mul-
tiple loops in an OEO would make the mode spacing greater,
which would ease the requirement for a high Q microwave fil-
ter [25]–[27]. However, an OEO with multiple loops would
have a poorer system stability and higher system cost. More
importantly, the frequency tunability would be complicated if
a multiple-loop structure is employed.
Recently, a technique to achieve an optically tunable OEO
with a wide frequency tunable range incorporating a tunable
microwave photonic filter implemented based on phase-mod-
ulation to intensity-modulation (PM-IM) conversion using
a phase-shifted fiber Bragg grating (PS-FBG) was proposed
[28], with the configuration shown in Fig. 7(a). When a mi-
crowave signal is applied to the PM, a phase-modulated opti-
cal signal consisting of an optical carrier and two first-order
sidebands are generated. When the phase-modulated light
wave is sent to the PS-FBG which has an notch in the reflec-
tion spectrum, if the optical wavelength is tuned such that one
sideband of the modulated optical signal falls into the notch
and is removed by the PS-FBG, the phase modulated signal
(a) (b)
fm
fm
2fmλ0
λ0 λ0
λ λ
fm
2fm
4fm
λ0 λ0
λ0
λ λ
LD LD
–1st
1st
–2nd 2nd
PD PD
Optical Fiber Optical Fiber
Dc bias Dc bias
MZM1 MZM1
Figure 4. Microwave signal generation based on external modulation using a MZM. (a) Frequency doubling by biasing the MZM at
the minimum transmission point. (b) Frequency doubling by biasing the MZM at the maximum transmission point. The optical car-
rier is removed by an optical notch filter.
LD TOPS PD
Microwave
Source
EDFA
DC bias
TEPS
Divider
PA1
PA2
DC bias
FBG
Notch
Filter
PC1 PC2
Output
MZM1 MZM2
Figure 5. A generalized microwave frequency multiplication system using two cascaded
MZMs. TOPS: tunable optical phase shifter, FBG: fiber Bragg grating, EDFA: erbium-
doped fiber amplifier, TEPS: tunable electrical phase shifter, PA: power amplifier.
Coupler
EA
LD
PC1 PC2
MZM
Electrical
Output
PD
Optical
Output
Coupler
Band-pass Filter
Figure 6. An opto-electronic oscillator.

4. becomes a single-sideband intensity-
modulated signal, thus PM-IM conver-
sion is achieved, and the joint operation
of the phase modulator and the PS-FBG
corresponds to a microwave photonic
filter, with the filter bandwidth deter-
mined by the bandwidth of the PS-FBG.
It is known that a PS-FBG can have a
notch as narrow as a few MHz, thus the
microwave photonic filter can effec-
tively select one eigenmode, making the
OEO operate in single frequency. The
frequency tuning can be simply done by
tuning the wavelength of the light wave
from the tunable laser source (TLS).
Thus, an OEO with a large frequency
tunable range is achieved. The opera-
tion of the microwave photonic filter is
shown in Fig. 7(b).
All-optical Microwave
Signal Processing
Introduction to Photonic Microwave
Delay-Line Filters
High-frequency and wideband microwave signals can also be
processed in the optical domain. The key signal processing
function is microwave filtering [29][30]. In this section, we
will review the techniques to implement photonic microwave
delay-line filters, with an emphasis on the generation of nega-
tive and complex coefficients to achieve bandpass filtering. The
use of nonuniform time delays to generate equivalent complex
coefficients to achieve photonic microwave delay-line filters
with an arbitrary spectral response will also be discussed.
Fig. 8(a) shows a generic photonic microwave delay-line
filter with a finite impulse response (FIR). As can be seen the
filter consists of a light source, a modulator, a delay-line mod-
ule, and a PD. Provided that the nonlinearity in the system is
small and negligible, the entire system can be considered as a
linear, time-invariant (LTI) system, in which the output ( )y t
can be written as
k( ) ( )y t a x t kT
k
N
0
1
= -
=
-
/ , (5)
where ( )x t is the microwave input signal, T is the time delay
difference between two adjacent taps, and ka is the coefficient
of the k-th tap.
Applying the Fourier transforms to both sides of (5), the
system transfer function is then obtained,
k( ) ( ),expH a j kT
k
N
0
1
~ ~= -
=
-
/ (6)
The time delay unit T determines the free spectral range
(FSR) of the microwave filter. The coefficient ak is proportional
(a) (b)
PS-FBG
OC
PC
ESA
Electrical PathOptical Path
TLS
SMF
OSA
OSA
1
2
3
PM1
PA PD
ω
MPF Frequency
Response
Reflection Spectrum Phase Response
0
ωe
First-Order
Sidebands
at Different
RF Frequencies
Optical
Carrier
Figure 7. (a) An optically tunable OEO. (b) The Illustration of the operation of the microwave photonic filter. Upper: The reflection
spectrum (dashed line) and phase response (solid line) of the PS-FBG. Lower: The frequency response of the microwave photonic
filter.
(a)
(b)
T
PD Output
Optical
Source
RF Input RF Output
RF
Modulator b0
b1
bN–1
1 × N N × 1
(N–1)T
T
PDMZM
MZM
Broaband
Optical Source
λ1 λ2 λ3 λ4
R4R3R2R1
λn
Rn
Figure 8. (a) A generic photonic microwave delay-line filter with a finite impulse response.
(b) The implementation of a photonic microwave delay-line filter using an FBG array.
April 2012 IEEE PHOTONICS SOCIETY NEWSLETTER 7

5. 8 IEEE PHOTONICS SOCIETY NEWSLETTER April 2012
to the optical intensity of the k-th tap and cannot be negative.
So the frequency response described by (6) is a typical transfer
function of a FIR delay-line filter with all-positive coefficients.
Fig. 8(b) shows an incoherent photonic microwave delay-
line filter using an FBG array. The microwave signal to be pro-
cessed is modulated on an incoherent optical wave, such as a
light wave from a light emitting diode (LED) or an amplified
spontaneous emission (ASE) source, which is then sent to an
FBG array. Due to the reflection of the FBGs in the FBG ar-
ray, light waves with different time delays are detected at the
PD. Since the optical source is incoherent, no optical interfer-
ence will be generated at the PD. The time-delayed optical
signals are then converted to time-delayed microwave signals.
The overall function of the system is equivalent to a delay-line
filter with the time delay difference determined by the physi-
cal separation of adjacent FBGs. The tap coefficients are set by
controlling the reflectivitie of the FBGs.
Photonic Microwave Delay-Line Filters with
Negative Coefficients
It is known a photonic microwave delay-line filter operating in
the incoherent regime would have all-positive tap coefficients.
Based on signal processing theory, an all-positive-coefficient
microwave delay-line filter can only operate as a low-pass fil-
ter. To overcome this limitation, considerable efforts have been
taken to design and implement photonic microwave delay-
line filters with negative or complex coefficients, to achieve
bandpass filtering functionality in the incoherent regime. A
straightforward solution to generate negative coefficients is
to use differential detection [31]. As shown in Fig. 9, a light
wave from an LD is modulated by a microwave signal, which is
then time delayed by optical fiber delay lines with a time delay
difference of T. The output signals from the fiber delay lines
are fed to a differential PD, which consists of two matched
PDs with the detected microwave signals combined and sub-
tracted electrically, leading to the generation of a positive and
a negative coefficient. The two-tap photonic microwave delay-
line filter shown in Fig. 9 can be extended to have N taps if
the single-wavelength source is replaced by an N wavelength
source and the 3-dB coupler is replaced by a 1 # N WDM
demultiplexer.
In Fig. 9, the negative coefficient is not generated directly
in the optical domain. The limitation of this technique is that
for a filter with N taps, N PDs are needed, making the filter
complicated and costly. A few techniques have been proposed
to implement an all-optical photonic microwave delay-line fil-
ter with negative coefficients using a single PD [32]–[37]. As
an example, negative coefficients can be generated using two
MZMs that are biased at the quadrature points of the comple-
mentary transmission slopes [37], as shown in Fig. 10. The op-
eration of the microwave phase inversion is shown in Fig. 10(a).
As can be seen, the two MZMs are biased at the linear regions
of the left and the right slopes of the transfer functions. When
a microwave signal is applied to the two MZMs, the envelopes
of the modulated optical signals are complementary. At the
output of a PD, two complementary microwave signals are
generated, leading to the generation of a negative coefficient.
A similar technique using only a single MZM was proposed
[38]. Considering the wavelength dependence nature of the
transfer function of the MZM, a proper dc bias would make the
modulator operate at the complementary slopes of the transfer
functions when the optical wavelengths are at 1550 nm and
1310 nm windows.
All the filters discussed above are implemented based on
the use of one or two MZMs. A photonic microwave bandpass
filter with negative coefficients can also be implemented based
on an optical phase modulator [39]. The negative coefficients
are generated based on phase modulation (PM) and PM-IM
conversion in two dispersive elements with complementary
dispersion profiles, such as linearly chirped FBGs (LCFBGs),
by reflecting the phase-modulated optical signals from the
LCFBGs with complementary chirp profiles, microwave sig-
nals without or with a phase inversion are generated at the PD.
An added advantage of using an optical phase modulator is
that a phase modulator is not biased, which eliminates the bias
drifting problem existing in a MZM-based system. The funda-
mental concept of the filter operation is shown in Fig. 11(a). An
RF signal is applied to the optical phase modulator via the RF
port to phase-modulate the multiple wavelengths at the phase
modulator. Since a PD functions as an envelope detector, if a
phase-modulated signal is directly applied to a PD, no modu-
lating signal will be detected except a dc. This conclusion can
also be explained based on the spectrum a phase-modulated
signal. As shown in Fig. 11(a), a small-signal phase-modulated
signal has a spectrum with the +1st and -1st order side-
bands out of phase. The beating between the optical carrier and
the +1st-order sideband exactly cancels the beating between
the optical carrier and the -1st-order sideband. However, if
the phase-modulated optical signal passes through a dispersive
element, the phase relationship between the two sidebands and
the optical carrier will be changed, leading to the conversion
from phase modulation to intensity modulation. In addition,
depending on the sign of the chromatic dispersion, a detected
RF signal with or without a phase inversion would be obtained,
leading to the generation of negative coefficients. The system
configuration of the filter is shown in Fig. 11(b).
Photonic Microwave Delay-Line Filters with
Complex Coefficients
The tunability of a photonic microwave delay-line filter is
usually achieved by adjusting the time-delay difference. How-
ever, the change of the time-delay difference would lead to
the change of the free spectral range (FSR), which results in
the change of the 3-dB bandwidth as well as the entire shape
of the frequency response. For many applications, it is highly
RF Input
1 × 2
Coupler
LD
a1
a0
T
PD
PD
–MZM
RF Output
Figure 9. A photonic microwave delay-line filter with a negative
coefficient using differential detection.

6. April 2012 IEEE PHOTONICS SOCIETY NEWSLETTER 9
desirable that only the center frequency of the passband or
stop-band is changed while maintaining the shape of the fre-
quency response unchanged. A solution to this problem is to
design a photonic microwave delay-line filter with complex
coefficients.
An N-tap microwave delay-line filter with complex coef-
ficients should have a transfer function given by
( )H a a e e a e e( ) ( )j j T
N
j N j N T
0 1 1
1 1
$ $g~ = + + +i ~ i ~- -
-
- - - -
a e en
jn j nT
n
N
0
1
$= i ~- -
=
-
/ (7)
where T is again the time delay different between two adjacent
taps. To tune the filter while maintaining the shape of the fre-
quency response, the phase shifts of all the taps should main-
tain a fixed relationship, as can be seen from (7). Therefore, the
phase shift of each tap should be tuned independently.
A photonic microwave delay-line filter with a complex co-
efficient using a wideband tunable optical RF phase shifter
was demonstrated. [40]. The RF phase shift is generated us-
ing two electro-optic MZMs by simply adjusting the bias
voltages applied to the two MZMs, and the phase shift re-
mains constant over the microwave frequency band of inter-
est. A wideband phase shifter can also be realized based on
a combined use of optical single-sideband modulation (SSB)
and stimulated Brillouin scattering (SBS). It was demonstrat-
ed that the phase of a microwave signal carried by an optical
carrier will experience microwave phase shift if the spectrum
of the optical carrier or the sideband is falling in the SBS gain
spectrum when passing through an optical fiber in which an
SBS is resulted [41].
Nonuniformly Spaced Photonic Microwave
Delay-Line Filters
The filters with complex coefficients in [40][41] have the
potential to be extended to have multiple taps, but the fil-
ter complexity would be significantly increased since each
tap needs a wideband phase shifter. To design a photonic
Pout / PinPout / Pin
VBIAS
VBIAS
V–
BIAS
V+
BIAS
Negative Slope
Positive Slope
(a)
V–
BIAS
V+
BIAS
(b)
2 × 1
Coupler
RF
Output
RF
Input
PC1
PC2
MZM 2
MZM 1
LD 2
LD 1
Dispersive
Device
PD
Figure 10. Photonic microwave delay-line filter with negative coefficients based on phase inversion using complementarily biased
intensity modulators. (a) The operation of phase inversion, (b) the schematic of the filter.

7. 10 IEEE PHOTONICS SOCIETY NEWSLETTER April 2012
microwave delay-line filter with complex coefficients having
a simple structure, a new concept was proposed by generat-
ing complex coefficients based on nonuniformly spaced taps
[42][43]. It was demonstrated that the complex coefficients
can be equivalently generated by introducing additional
time delays to the taps.
As given in (6), the frequency response of a uniformly-
spaced microwave delay-line filter has a frequency response
is given by k ( )exp( ) a j kTH N 1
/ ~~ -= -
k 0=
. As can be seen
( )H ~ has a multi-channel frequency response with adjacent
channels separated by an FSR, with the mth channel located
at m~ X= .
In a regular photonic microwave delay-line filter based on
incoherent detection, the coefficients are usually all positive,
or special designs have to be employed to generate negative
or complex coefficients. However, a phase term can be intro-
duced to a specific coefficient by adding an additional time
delay at the specific tap, which is termed time-delay-based
phase shift. For example, at m~ X= a time delay shift of
Tx will generate a phase shift given by m#TT{ x X=- .
Note that such a phase shift is frequency-dependent, which
is accurate only for the frequency at ,mX but approximately
accurate for a narrow frequency band at around .mX For
most of applications, the filter is designed to have a very
narrow frequency band, therefore, for the frequency band of
interest, the phase shift can be considered constant over the
entire bandwidth. As a result, if the m th bandpass response,
where ,m 0! is considered, one can then achieve the desired
phase shift at the kth tap by adjusting the time delay shift by
.kTx Considering the time delay shift of ,kTx one can get
the frequency response of the nonuniformly-spaced delay-
line filter at around ,m~ X=
k( ) expH a j k 2
Non
k
N
k
0
1
T~ r x ~
X
= - +
=
-
` j8 B/
( )exp expa jm jk 2
k k
k
N
0
1
#T. x r ~X
X
- -
=
-
` j6 @/ (8)
As can be seen from (8), an equivalent phase shift is gener-
ated for each tap coefficient. Specifically, if the desired phase
shift for the kth tap is k{ , the total time delay kx for the kth
tap is /kT mk kx { X= - . As a result, if the time delay of each
tap is adjusted, the filter coefficients would have the required
phase shifts to generate the required passband with the desired
bandpass characteristics.
The design of a nonuniformly-spaced photonic microwave de-
lay-line filter to achieve a bandpass filter with a flat top was demon-
strated [42]. The technique is particularly useful for advanced mi-
crowave signal processing. For example, the use of a nonuniformly
spaced photonic microwave delay-line filter to achieve microwave
phase coding [44], chirped microwave pulse generation [45], mi-
crowave pulse compression [46], microwave differentiation [47],
and microwave Hilbert transformation [48] has been reported.
Conclusion
An overview about optical generation of microwave signals and all-
opticalmicrowavesignalprocessingwaspresented.Thekeysignifi-
cance of using photonics to generate and process microwave signals
is that high-frequency microwave signals can be generated and pro-
cessed in the optical domain which may not be possible using the
state-of-the-art electronics. In addition, the
generated and processed microwave signals
can be distributed over optical fiber for long
distance distribution, to take advantage of
the extremely low loss of the state-of-the-
art fiber, which is an added advantage of
photonic techniques for the generation and
processing of microwave signals.
References
1. J. P. Yao “Microwave photonics,” J.
Lightw. Technol., vol. 27, no. 3, pp.
314–335, Feb. 2009.
2. L. Goldberg, H. F. Taylor, J. F. Weller,
and D. M. Bloom, “Microwave signal
generation with injection locked la-
ser diodes,” Electron. Lett., vol. 19, no.
13, pp. 491–493, Jun. 1983.
3. L. Goldberg, A. Yurek, H. F. Taylor,
and J. F. Weller, “35 GHz micro-
wave signal generation with injection
locked laser diode,” Electron Lett., vol.
21, no. 18, pp. 714–715, Aug. 1985.
4. J. Harrison and A. Mooradian, “Line-
width and offset frequency locking
of external cavity GaAlAs lasers,”
IEEE J. Quantum Electron., vol. 25,
no. 6, pp. 1252–1255, Jun. 1989.
Figure 11. (a) RF phase inversion based on phase modulation and PM-IM conversion
through opposite dispersions. (b) A photonic microwave delay-line filter with a nega-
tive coefficient based on PM-IM conversion in two LCFBGs with opposite dispersions.
(a)
(b)
LD 1
PM
RF
Input
RF
Output
LCFBG 2 (+)
LCFBG 1 (–)
LD N
Mux
DeMux
t
t
ωc–ωm
ωc
ωc+ωm
ωc–ωm
ωc–ωm
ωc
ωc
ωc–ωm
ωc
ωc+ωm
ωc+ωm
ωc+ωm
PD
PD
PD
Dispersive Device
D > 0
Dispersive Device
D < 0

8. April 2012 IEEE PHOTONICS SOCIETY NEWSLETTER 11
5. R. T. Ramos and A. J. Seeds, “Fast heterodyne optical
phase-lock loop using double quantum well laser diodes,”
Electron. Lett., vol. 28, no. 1, pp. 82–83, Jan. 1992.
6. U. Gliese, T. N. Nielsen, M. Bruun, E. Lintz Christensen,
K. E. Stubkjaer, S. Lindgren, and B. Broberg, “A wide-
band heterodyne optical phase-locked loop for generation
of 3-18 GHz microwave carriers,” IEEE Photon. Technol.
Lett., vol. 4, no. 8, pp. 936–938, Aug. 1992.
7. A. C. Bordonalli, C. Walton, and A. J. Seeds, “High-Per-
formance phase locking of wide linewidth semiconductor
lasers by combined use of optical injection locking and
optical phase-lock loop,” J. Lightwave Technol., vol. 17, no.
2, pp. 328–342, Feb. 1999.
8. K. J. Williams, “6-34 GHz offset phase locking of Nd:
YAG 1319 nm nonplanar ring lasers,” Electron. Lett., vol.
25, no. 18, pp. 1242–1243, Aug. 1989.
9. Z. F. Fan and M. Dagenais, “Optical Generation of a
mHz-Linewidth microwave signal using semiconductor
lasers and a discriminator-aided phase-locked loop,” IEEE
Trans. Microwave Theory Tech., vol. 45, no. 8, pp. 1296–
1300, Aug. 1997.
10. H. Rideout, J. Seregelyi, S. Paquet, and J. P. Yao, “Dis-
criminator-aided optical phase-lock loop incorporating a
frequency down-conversion module,” IEEE Photon. Tech-
nol. Lett., vol. 18, no. 22, pp. 2344–2346, Nov. 2006.
11. P. Shen, N. J. Gomes, P. A. Davies, W. P. Shillue, P. G.
Huggard, and B. N. Ellison, “High-purity millimeter-
wave photonic local oscillator generation and delivery,” in
Proc. Int. Microwave Photonics Topical Meeting, Sep. 10–12,
2003, pp. 189–192.
12. G. Qi, J. P. Yao, J. Seregelyi, C. Bélisle, and S. Paquet,
“Generation and distribution of a wide-band continuously
tunable mm-wave signal with an optical external modula-
tion technique,” IEEE Trans. Microw. Theory Tech., vol. 53,
no. 10, pp. 3090–3097, Oct. 2005.
13. T. Kawanishi, H. Kiuchi, M. Yamada, T. Sakamoto, M.
Tsuchiya, J. Amagai, and M. Izutsu, “Quadruple frequency
double sideband carrier suppressed modulation using high ex-
tinction ratio optical modulators for photonic local oscillators,”
in Proc. IEEE Microwave Photonics Conf. pp. 1–4, Oct. 2005.
14. J. Zhang, H. Chen, M. Chen, T. Wang, S. Xie, “A pho-
tonic microwave frequency quadrupler using two cascaded
intensity modulators with repetitious optical carrier sup-
pression,” IEEE Photon. Technol. Lett., vol. 19, no. 14, pp.
1057–1059, Jul. 2007.
15. Y. Zhao, X. Zheng, H. Wen, and H. Zhang, “Simplified op-
tical millimeter-wave generation configuration by frequency
quadrupling using two cascaded Mach–Zehnder modula-
tors,” Opt. Lett., vol. 34, no. 21, pp. 3250–3252, Nov. 2009.
16. M. Mohamed, X. Zhang, B. Hraimel, and K. Wu, “Fre-
quency sextupler for millimeter-wave over fiber systems,”
Opt. Express, vol. 16, no. 14, pp. 10141–10151, Jun. 2008.
17. J. Zhang, H. Chen, M. Chen, T. Wang, and S. Xie, “Pho-
tonic generation of a millimeter-wave signal based on
sextuple-frequency multiplication,” Opt. Lett., vol. 32, no.
9, pp. 1020–1022, Apr. 2007.
18. W. Li and J. P. Yao, “Microwave frequency multiplica-
tion using two cascaded Mach-Zehnder modulators,”
Proc. 2009 Asia-Pacific Microwave Photonics Conf., Beijing,
China, Apr. 2009.
19. J. Ma, X. Xin, J. Yu, C. Yu, K. Wang, H. Huang, and L.
Rao, “Optical millimeter wave generated by octupling the
frequency of the local oscillator,” J. Opt. Netw. vol. 7, no.
10, pp. 837–845, Oct. 2008.
20. C. Lin, P. Shih, W. Jiang, J. Chen, P. Peng, and S. Chi,
“A continuously tunable and filterless optical millimeter-
wave generation via frequency octupling,” Opt. Express,
vol. 17, no. 22, pp. 19749–19756, Oct. 2009.
21. W. Li and J. P. Yao, “Microwave generation based on
optical-domain microwave frequency octupling,” IEEE
Photon. Technol. Lett. vol. 22, no. 1, pp. 24–26, Jan. 2010.
22. W. Li and J. P. Yao, “Investigation of photonically assisted
microwave frequency multiplication based on external
modulation,” IEEE Trans. Microw. Theory Tech., vol. 58,
no. 11, pp. 3259–3268, Nov. 2010.
23. W. Li and J. P. Yao, “Microwave and terahertz generation
based on photonically assisted microwave frequency twel-
vetupling with large tunability,” IEEE Photon. J., vol. 2,
no. 6, pp. 954–959, Dec. 2010.
24. X. S. Yao and L. Maleki, “Converting light into spectrally
pure microwave oscillation,” Opt. Lett., 21, 483 (1996).
25. X. S. Yao and L. Maleki, “Multiloop optoelectronic os-
cillator,” IEEE J. Quantum Electron., vol. 36, no. 1, pp.
79–84, Jan. 2000.
26. Y. Jiang , J. Yu , Y. Wang, L. Zhang, and E. Yang “An
optical domain combined dual-loop optoelectronic os-
cillator,” IEEE Photon. Technol. Lett., vol. 19, no. 11, pp.
807–809, Jun, 2007.
27. E. Shumakher and G. Eisenstein, “A novel multiloop op-
toelectronic oscillator,” IEEE Photon. Technol. Lett., vol. 20,
no. 22, pp. 1881–1883, Nov. 2008.
28. W. Li and J. P. Yao, “An optically tunable frequency-
doubling optoelectronic oscillator incorporating a phase-
shifted-fiber-Bragg-grating-based frequency-tunable
photonic microwave filter,” 2011 IEEE Microwave Photonics
Conf., Singapore, Oct. 2011, pp. 429–432.
29. J. Capmany, B. Ortega, and D. Pastor, “A tutorial on mi-
crowave photonic filters,” J. Lightw. Technol., vol. 24, no.
1, pp. 201–229, Jan. 2006.
30. R. A. Minasian, “Photonic signal processing of microwave
signals,” IEEE Trans. Microw. Theory Tech., vol. 54, no. 2,
pp. 832–846, Feb. 2006.
31. S. Sales, J. Capmany, J. Marti, and D. Pastor, “Experi-
mental demonstration of fiber-optic delay line filters with
negative coefficients,” Electron. Lett., vol. 31, no. 13, pp.
1095–1096, Jun. 1995.
32. F. Coppinger, S. Yegnanarayanan, P. D. Trinh, and B.
Jalali, “All-optical RF filter using amplitude inversion in
a semiconductor optical amplifier,” IEEE Trans. Microw.
Theory Tech., vol. 45, no. 8, pp. 1473–1477, Aug. 1997.
33. T. Mukai, K. Inoue, and T. Saitoh, “Homogeneous gain
saturation in 1.5 m InGaAsP traveling-wave semiconduc-
tor laser amplifiers,” Appl. Phys. Lett., vol. 51, no. 6, pp.
381–383, Aug. 1987.
34. X. Wang and K. T. Chan, “Tunable all-optical inco-
herent bipolar delay-line filter using injection-locked

9. Fabry-Perot laser and fiber Bragg gratings,” Electron. Lett.,
vol. 36, no. 24, pp. 2001–2002, Nov. 2000.
35. S. Li, K. S. Chiang, W. A. Gambling, Y. Liu, L. Zhang,
and I. Bennion, “A novel tunable all-optical incoherent
negative-tap fiber-optical transversal filter based on a
DFB laser diode and fiber Bragg gratings,” IEEE Photon.
Technol. Lett., vol. 12, no. 9, pp. 1207–1209, Sep. 2000.
36. J. Mora, M. V. Andres, J. L. Cruz, B. Ortega, J. Capmany, D.
Pastor, and S. Sales, “Tunable all-optical negative multitap
microwave filters based on uniform fiber Bragg gratings,”
Opt. Lett., vol. 28, no. 15, pp. 1308–1310, Aug. 2003.
37. J. Capmany, D. Pastor, A. Martinez, B. Ortega, and S.
Sales, “Microwave photonics filter with negative coeffi-
cients based on phase inversion in an electro-optic modula-
tor,” Opt. Lett., vol. 28, no. 16, pp. 1415–1417, Aug. 2003.
38. B. Vidal, J. L. Corral, and J. Marti, “All-optical WDM
multi-tap microwave filter with flat bandpass,” Opt. Ex-
press, vol. 14, no. 2, pp. 581–586, Jan. 2006.
39. F. Zeng, J. Wang, and J. P. Yao, “All-optical microwave
bandpass filter with negative coefficients based on a phase
modulator and linearly chirped fiber Bragg gratings,” Opt.
Lett., vol. 30, no. 17, pp. 2203–2205, Sep. 2005.
40. Y. Yan and J. P. Yao, “A tunable photonic microwave fil-
ter with a complex coefficient using an optical RF phase
shifter,” IEEE Photon. Technol. Lett., vol. 19, no. 19, pp.
1472–1474, Sep. 2007.
41. A. Loayssa, J. Capmany, M. Sagues, and J. Mora, “Demon-
stration of incoherent microwave photonic filters with all-
optical complex coefficients,” IEEE Photon. Technol. Lett.,
vol. 18, no. 16, pp. 1744–1746, Aug. 2006.
42. Y. Dai and J. P. Yao, “Nonuniformly-spaced photonic mi-
crowave delay-line filter,” Opt. Express, vol. 16, no. 7, pp.
4713–4718, Mar. 2008.
43. Y. Dai and J. P. Yao, “Nonuniformly spaced photonic mi-
crowave delay-line filters and applications,” IEEE Trans.
Microw. Theory Tech., vol. 58, no. 11, pp. 3279–3289, Nov.
2010.
44. Y. Dai and J. P. Yao, “Microwave pulse phase encoding us-
ing a photonic microwave delay-line filter,” Opt. Lett., vol.
32, no. 24, p. 3486–3488, Dec. 2007.
45. Y. Dai and J. P. Yao, “Chirped microwave pulse genera-
tion using a photonic microwave delay-line filter with a
quadratic phase response,” IEEE Photon. Technol. Lett., vol.
21, no. 9, pp. 569–571, May 2009.
46. Y. Dai and J. P. Yao, “Microwave correlator based on a
nonuniformly spaced photonic microwave delay-line fil-
ter,” IEEE Photon. Technol. Lett., vol. 21, no. 14, pp. 969–
971, Jul. 2009.
47. Y. Han, Z. Li, and J. P. Yao “A microwave bandpass dif-
ferentiator implemented based on a nonuniformly-spaced
photonic microwave delay-line filter,” J. Lightw. Technol.,
vol. 29, no. 22, pp. 3470–3475, Nov. 2011.
48. Z. Li, Y. Han, H. Chi, X. Zhang, and J. P. Yao, “A contin-
uously tunable microwave fractional Hilbert transformer
based on a nonuniformly-spaced photonic microwave
delay-Linefilte r,” J. Lightw. Technol., to appear.
12 IEEE PHOTONICS SOCIETY NEWSLETTER April 2012